[Qgis-user] Re: Interpolation plugin

Marco Hugentobler marco at hugis.net
Tue Jan 26 06:52:57 EST 2010


Hi Viktor

> 1) Is there a possibility in QGIS to use *polyline *layer as a source of
> interpolation (TIN creation)? If no, is it possible to add this
> functionality in the future?

Yes. Additionally, you may set in the 'type' combo if the plugin should just 
consider the vertices or treat the lines as structure lines / break lines

> 2) Is there a possibility in QGIS to *limit* interpolation borders by
> another polygonal non-heights layer (such as Arc/Info 'soft clip')?

At the moment not

> 3) What is a dimension of cell coordinates? Are they use the same units as
> projected point layer units?

They are the same as the (unprojected) layer units. The interpolation plugin 
just considers the layer and not the projection of the canvas map.

> 4) Which format QGIS saves TIN in?

ASCII grid (text format). I know this is not optimal for large datasets. 
Patches are welcome to extend the hardcoded grid file writing 
(qgsgridfilewriter) with a solution that uses available GDAL drivers for grid 
file writing.

Regards,
Marco


Am Dienstag, 26. Januar 2010 12.10:40 schrieb Viktor Kolesnyk:
> Hi!
> 
> I was using Arc/Info under Windows XP and now I migrated to Linux Gentoo
>  and want to migrate to QGIS.
> 
> One of the tasks I used Arc/Info for is *height (elevation) matrix
>  creation*. I have polyline and point layers as sources. The former layer
>  is more accurate.
> In Arc/Info I did it in two steps:
> 1) TIN creation from polyline layer. I also use a territory polygonal layer
> to limit interpolation borders (so called '*soft clip*').
> 2) Convert TIN to Raster (in Arc/Info Binary Grid, *.adf) with 100*100
> meters cell size.
> As a result I had 547 Mb raster layer *.adf file and some smaller
> informative *.adf files.
> 
> I read QGIS 1.3.0 user guide and Marco's "Terrain Modelling with Triangle
> Based Free-Form Surfaces" thesis and
> as I understand there is only possibility to use point layers to create TIN
> in QGIS?!
> So, I tried this functionality in QGIS 1.4.0 under Gentoo Linux.
> I projected my point layer from Geographical Coordinate System to Projected
> CS (WGS84).
> Then set it as the source in Interpolation Plugin window and chose 100*100
> (as I understand in meters) cell size of output layer.
> I don't know which format QGIS saves TIN in and there is no filters of file
> extensions in "Save interpolated layer as..." window.
> So, I simply chose "tin.adf". As a result of interpolation I have 2,5 Gb
> file, that seems to be less accurately than my 547 Mb Arc/Info Binary grid
> one.
> 
> Some questions:
> 1) Is there a possibility in QGIS to use *polyline *layer as a source of
> interpolation (TIN creation)? If no, is it possible to add this
> functionality in the future?
> 2) Is there a possibility in QGIS to *limit* interpolation borders by
> another polygonal non-heights layer (such as Arc/Info 'soft clip')?
> 3) What is a dimension of cell coordinates? Are they use the same units as
> projected point layer units?
> 4) Which format QGIS saves TIN in?
> 

-- 
Dr. Marco Hugentobler
HUGIS - GIS programming and consulting
Webereistrasse 66
CH-8134 Adliswil
marco at hugis.net
http://homepage.hispeed.ch/hugis
Technical Advisor QGIS Project Steering Committee


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